IsValidDomainName is a primitive domain name checker taken from go standard library.

IsValidUnixUser returns true if passed string can be used to create a valid UNIX user.

Split splits the string v using delimiter rune.

SplitAt splits array of strings at a given separator.

SplitComma splits a comma-delimted string, comma can be escaped using '\' escape rune.

WithoutFlag removes the flag from the argument list.